1. Field of the Invention
The present invention relates to a fixing device for use in an image forming apparatus such as a copier, a fax, or a printer.
2. Description of the Background Art
Generally, an image forming apparatus such as a printer performs an image formation to a sheet by transferring a toner image formed on a photosensitive drum onto the sheet, followed by fixing the toner image on the sheet.
A fixing unit adapted to fix a toner image generally has a pair of fixing rollers which are heated and pressurized. The toner image is fixed by allowing a sheet to pass a nip area defined by the fixing roller pair. The fixing unit is likely to cause a sheet jam because the sheet is heated and pressurized while passing the fixing unit. In view of this, there is provided a sheet detection arm, at a downstream position of the fixing roller pair, for detecting a sheet to be discharged from the fixing roller pair.
In order to facilitate a user to remove a jammed sheet, for instance, an image forming apparatus designed for single-sided printing, e.g. disclosed in Japanese Unexamined Patent Publication No. 2005-55817, has an openable/closable fixing cover for covering a fixing roller pair.
Also, in recent years, image forming apparatuses capable of double-sided printing onto a sheet have been widespread. In such image forming apparatuses, there is defined a backward transport path, at a position below a fixing roller pair, for transporting a sheet discharged from the fixing roller pair to an image forming unit again.
In the image forming apparatuses capable of double-sided printing, there is provided a sheet detection arm for detecting transport of a sheet in a forward transport path and in the backward transport path after the sheet is discharged from the fixing roller pair. The sheet detection arm is a pivotal member, with one end thereof extending in the forward transport path, and the other end thereof extending in the backward transport path. The sheet detection arm is a single member adapted to detect the sheet transport in the two transport paths disposed vertically away from each other. Thus, the sheet detection by the single member enables to suppress increase of the number of parts constituting the image forming apparatus, and to reduce the dimensions of the image forming apparatus.
Similarly to the image forming apparatus adapted for single-sided printing, as recited in the above publication, it is desirable to provide an openable/closable fixing cover in the image forming apparatus capable of double-sided printing in order to facilitate a jammed sheet removal.
If, however, the openable/closable fixing cover is provided in the image forming apparatus capable of double-sided printing, the sheet detection arm is provided on the fixing cover, because a part of the fixing cover defines the forward transport path and the backward transport path. In this arrangement, in opening the fixing cover, the other end of the sheet detection arm extending in the backward transport path may be abutted against a lower guide constituting the backward transport path, which may cause breakage or damage of the sheet detection arm.
Thus, in a fixing device provided with the sheet detection arm for detecting a sheet in the two transport paths i.e. the forward transport path and the backward transport path, the sheet detection arm may be damaged in opening the openable/closable fixing cover.